Hot forming is a known and frequently used method for the plastic deformation of metal materials. In contrast with cold forming, hot forming takes place at temperatures above the recrystallization temperature of the material that is to undergo the forming, so that even very high degrees of forming can be achieved. Owing to the heating of the workpieces that is required for the hot forming, there is the risk that parts of the coating will peel away and stick to the heated workpieces as contamination. Such contaminants may damage the (pressing) tool during a subsequent hot-forming operation or reduce the surface quality and dimensional accuracy of the components produced, and should therefore be avoided.
DE 10 2007 012 180 B3 for example discloses a method for the heat treatment of semi-finished metal products in a continuous furnace. The continuous furnace described has two zones, which when looking in the direction in which the workpiece is fed through the furnace, are arranged one behind the other and which are largely separated from one another by an intermediate wall. The intermediate wall can be displaced, so that its position can be adapted to the size of the semi-finished products that are transported through the furnace. Heaters are provided in both zones of the continuous furnace, and are configured as gas burners with which different temperatures can be set in the two zones.
According to the teaching of DE 10 2007 012 180 B3, a fan may be provided on the upper side in each of the two zones by which an air stream can be generated and directed onto the semi-finished products that are located in the zone. The furnace has feed lines, with which air or an inert gas can be fed in from the outside. There are also return lines, with which gas can be drawn off out of the furnace and returned into the furnace again—that is to say recirculated. In this case, a cooling of the recirculated gas may take place. Both lines open out into the furnace in the region of the fans. Therefore, the fans and the feed and return lines mean that there are different possibilities for treating the semi-finished products. After the heated semi-finished products leave the continuous furnace, the semi-finished products are to be fed to a downstream treatment or forming process.
The solution that is known from DE 10 2007 012 180 B3 has various disadvantages. One disadvantage of the solution described is that the air stream generated by the fans always impinges on the semi-finished products perpendicularly, that is to say at an angle of approximately 90°. Other angles, on the other hand, which may for example be desirable for reasons of flow mechanics, cannot be set. Another disadvantage is that a directed pressurized jet cannot be generated by the fans, but only a turbulent air stream with a very low pressure.